Method of impregnating products with liquid agents



Jan. 30, 1940. MERRIAM 2,188,371

METHOD OF IHPREGNATING PRODUCTS WITH LIQUID AGENTS Filed Sept. 15, 1938Patented Jan. 30, 1940 PATENT OFFICE METHOD OF IDIPREGNATING PRODUCTSWITH LIQUID AGENTS Charles J. Merriam, Winnetka, Ill., assignor to TheGuardite Corporation, a corporation of Illinois Application September15, 1938, Serial No. 230,111

7 Claims.

This invention relates to an improved method of impregnating productswith a liquid agent.

In Patent 2,080,179, Russell Wiles and I have disclosed a method offreeing bulk products from non-condensible gas in order to permit theintroduction of fumigant or other agent, and particularly of moisture.In that patent the material is subjected without the addition of heat,to a vacuum sufliciently high to boil water from the material at itsnormal temperature, and the evacuation continued long enough to washfrom the material all residual air. Thereafter the product is free toreceive any fluid impregnating agent.

In moistening material, however, there is a limit to the amount ofmoisture which may be added in the form of steam, inasmuch as thecondensation of the steam necessarily raises the temperature of the bulkproduct and with organic materials a few percent of moisture added inthis fashion generally or frequently brings the temperature toundesirable heights. For instance wheat increases from 'to F. for eachpercent moisture condensed from steam.

The repetition of steaming cycles does no good, because the amount ofmoisture removed by evaporation in cooling the material is equal to theamount added in procuring the equivalent increase in temperature.

In accordance with the present invention means are provided by which anindefinite amount of moisture may be added to bulk products within anygiven temperature range. This is accomplished by the use of steam athigh temperatures and pressures at which it has less heat content thanis necessary to expand it to a low temperature and pressure. It isparticular- 1y preferred to employ steam above the critical temperature(about 374 C. 706 F.) and above or near the critical pressure (about3226 lbs. per sq. in. Abs).

At this temperature the steam has a calorific content in theneighborhood of 925 B. t. u.s per pound, whereas the same amount ofsteam at 150 F. and the equivalent pressure (about 3.7 lbs.) has a heatcontent of about 1125 B. t. u.s. This means that the deficiency has tobe supplied by condensation of moisture inthe steam, or its equivalent,where steam at the-higher uum sufilciently high to evacuate watertheretemperature and pressure is expanded to the from, and theevacuation is continued long enough to lower the temperature of thetobacco say, 8-15 F. (from, say, to 65 F.), the vacuum for this purposereaching around 29.7 inches of mercury (on the basis of a thirty-inch 6barometer) and then steam at 706 F. and 3226 lbs. pressure is introduceduntil the temperature in the tobacco has reached F. the moisture pickedup will be substantially more than would be added by the use of ordinarysteam. Moreover, by evaporating some of the condensed moisture, tomarkedly reduce the temperature, and then repeating the steamingoperation with the supercritical steam a further gain may beaccomplished. The cycle may of course be 15 repeated as often asdesired, there being a gain each time of 10 to 20% on the total wateradded by the step. Normally the temperature will be lowered 15-60 F. oneach evacuation step.

With tobacco it is generally preferable not 20 to exceed F., and for themany types of tobacco lower limits are observed. Many organic productsshould not exceed 212 F. and of course, many are heat susceptible attemperatures far lower.

It is preferred that the steam be introduced as close as possible to thematerial to be treated, in order that the material rather than theevacuating equipment or the nozzles obtain the benefit of therefrigeration.

The process is applicable primarily to organlc products in bulk, but itmay be used in any case where the ordinary impregnation methods fan. Itis particularly valuable with tobacco in bales or hogsheads, but may beemployed to advantage with grain such as wheat, or other organicmaterials.

While the invention is primarily useful in connection with water, due tothe high latent heat thereof, it may be used with other gaseswhere suchuse becomes necessary or desirable.

The amount of vaporized liquid, such as steam, is generally smallcompared to the amount of material being treated. The amount is ofcourse not such as to raise the pressure to anything approaching thepressure of the gas used. For most purposes the final pressure will bebelow atmospheric, or at least close to it because of the nature of theproducts generally employed. Pressures of several atmospheres however,do not 50 greatly affect the refrigerating effect.

In any event, the final pressure is always one sufficiently low tohave'permitted expansionenough to obtain a substantial refrigeratingeffect from the gas.

A diagrammatic pressure time graph is shown in the drawing. The pointmarked A illustrates the break in the curve when water begins to boilfrom the tobacco upon lowering of the pressure to a point equal to thevapor pressure of the water in the tobacco. The point B represents thepoint at which supercritical steam is introduced; the line 3-0represents the rise in pressure during the steaming operation; the lineC-D represents the evacuation curve followin the steaming, the slope ofthis curve having been somewhat steepened in order to get the diagram onone page; the line D-E represents a subsequent steaming operation withsupercritical steam; the line E--F is a subsequent evacuation curve,likewise steepened; and the line F-G represents a third steamingoperation with supercritical steam. The time intervals will. of course,de'pendupon the supply of steam and the capacity of the evacuatingequipment. 4

The foregoing detailed description has bee given for ciearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom.

I claim:

1. The method of liquid impregnating a product which comprisessubstantially freeing it from noncondensible gas and then introducingthereto a substantially saturated gas at a temperature' and pressure atleast approaching the critical, and markedly above the temperature andpressure of the product, whereby the temperature ofthe product is raisedby condensation of gas thereon.

2. The method of moistening an organic product in bulk which comprisesfreeing the product substantially from noncondensible gas and producinga subatmospheric pressure thereon, and introducing substantiallysaturated steam at a temperature and pressure at least approaching thecritical to raise the temperature and pressure upon the material.

3. The. method as set forth in claim 2 in which the final temperature ofthe product is less than 212 F.

4. The method as set forth in claim 2 in which the product is tobaccoand the final temperature is below 190 F.

5. The method as set forthin claim 2 in which the product is tobacco.

6. The method which comprises subjecting a bulk product withoutsubstantial addition of heat, to a vacuum sufliciently high to causecontained moisture in the product to boil, continuing the evacuation towash substantially all non ccndensible gas from the product, and thenintroducing steam at substantially its critical temperature and pressurethereto to increase the pressure to a higher, but subatmosphericpressure.

7. The method as set forth in claim 6 in which the product is againsubjected to a vacuum sufficient to cause boiling of contained moisture,the evacuation is continued until the temperature of the product hasbeen markedly reduced, and the steaming step is then repeated wherebythe moisture content of the product is progressively increased in eachcycle.

CHARLES J. BEER-1AM.

